This invention relates generally to the field of fuel nozzles and, more particularly, to a dual-mode flame holding, Up-cooled combustion engine fuel nozzle.
Combustion engines are machines that convert chemical energy stored in fuel into mechanical energy useful for generating electricity, producing thrust, or otherwise doing work. These engines typically include several cooperative sections that contribute in some way to this energy conversion process. In gas turbine engines, air discharged from a compressor section and fuel introduced from a fuel supply are mixed together and burned in a combustion section. The products of combustion are harnessed and directed through a turbine section, where they expand and turn a central rotor. The rotor produces shaft horsepower or torque; this output shaft may, in turn, be linked to devices such as an electric generator to produce electricity.
As the need for electricity rises, so to do the performance demands made upon industrial turbine combustion engines. Increasingly, these engines are expected to operate at increased levels of efficiency, while producing only minimal amounts of unwanted emissions. Various approaches have been undertaken to help achieve these results.
One approach has been to utilize multiple single-mode nozzles arranged in discrete groups to form a so-called xe2x80x9cdry, low-NOxxe2x80x9d (DLN) combustor. DLN combustors typically provide lowered amounts of unwanted emissions by lowering the burning temperature and by premixing fuel and air providing independent flows of fuel to two or more discrete groups or xe2x80x9cstagesxe2x80x9d of combustors, with each stage contributing in a different manner to the overall combustion process. Two common stages found in DLN arrangements are the xe2x80x9cpilotxe2x80x9d and xe2x80x9cmainxe2x80x9d stages. Quite often, the pilot stage is a xe2x80x9cdiffusionxe2x80x9d nozzle capable of holding a flame. Diffusion-type nozzles are quite stable, but they inherently include fuel-rich regions which provide a source of combustion hot spots that lead to the formation of unwanted NOx emissions. To keep these NOx emissions at a minimum, typically only one diffusion nozzle is used in a given combustor. The main stage nozzles operate in a xe2x80x9cpremixxe2x80x9d mode, producing a mixture of fuel and air that bums through interaction with other flames, such as the fuel-rich flame produced by the pilot stage. This arrangement is stable and produces relatively-low NOx emissions, when compared to earlier approaches. However, the diffusion-type pilot nozzle produces localized regions of high temperature or xe2x80x9chot spotsxe2x80x9d and remains a source of unwanted NOx emissions, making this approach unsuitable for some settings.
In an attempt to reduce NOx emissions even further, various attempts to make DLN combustors having pilot nozzles with a reduced reliance on diffusion-type flames have been made. In some cases, these efforts have focused on nozzles capable of operating in both diffusion and xe2x80x9cpremixxe2x80x9d modes. Efforts to produce such a nozzle have met with difficulty. This type of nozzle must not only be able to produce a controlled stream of mixed fuel and air, it must also be able to dispense fuel for operation in a diffusion-mode and provide tip cooling to avoid melting as combustion temperatures rise to meet increased demands for power output. Nozzles attempting to provide these characteristics have succeeded to varying degrees. For a variety of reasons, however, the practical difficulties imposed by meeting these requirements simultaneously has resulted in nozzles that are prone to leaks, are not reliable, and which may actually reduce efficiency due to losses generated by a large number of components.
Accordingly, there exists a need for a dual-mode, flame-stable nozzle that provides tip cooling and selectively dispense diffusion fuel or a mixture of fuel and air in a simplified manner. The nozzle should transmit cooling air passively, through a dedicated passage that eliminates the need for complex valve arrangements. The nozzle should also include discrete fluid-guiding conduits that are sealed in a leak-resistant manner with reduced reliance upon sliding joints and bellows arrangements.
The instant invention is a dual-mode, flame-holding nozzle for a gas turbine combustion engine that provides passive tip cooling and selective dispersion of diffusion fuel or mixed fuel and air. The nozzle includes several elongated sleeves that cooperatively form discrete passageways adapted to transmit fluids through the nozzle. The nozzle includes conduits that allow fuel and cooling air to reach designated fuel and cooling passageways without mixing. This arrangement advantageously ensures that air used to cool the nozzle does not become flammable, thereby reducing the chances of unwanted flashback occurrences. Portions of the nozzle sleeves are also strategically arranged to transmit fluids in a manner that provides substantially-uniform thermal expansion, thereby reducing the need for sliding joints and/or bellows arrangements.
Accordingly, it is an object of the present invention to provide a dual-mode combustor nozzle having passive tip cooling and controlled flameholding capabilities.
It is another object of the present invention to provide a dual-mode combustor nozzle that includes a dedicated cooling fluid passageway that operates without complex valve or manifold arrangements.
It is another object of the present invention to provide a dual-mode combustor nozzle that includes discrete fluid-guiding regions that are sealed with a reduced need for sliding joints or bellows arrangements.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.